vectorizing/simplifying randperm code

Hi

The idea of my code is the following:

If for instance I have the three "sequences":

(1) 12345 (2) 56789 (3) 43789

And an array of length n, my algorithm choses one of the three sequences at random for array(1). For array(2) the algorithm should chose one of the not yet chosen sequences at random, and array(3) takes the left-over sequence. For array(4) (i.e. arrar(number of sequences +1) the entire procedure restarts. Below my code - could it be done any better/faster?

function x = RandomizeTrials(numberofSeq, lengthofArray, SequenceArray)

   N = lengthofArray/numberofSeq; 
   x = []; 
   for i=1:N
     x = [x randperm(numberofSeq)]; 
   end

   for i = 1:length(SequenceArray)
       for j = 1:length(x)
       if x(j) == i
           x(j) = SequenceArray(i);
       end
       end
   end

end